How to calculate the signal that a load cell delivers by division (μV/div)?

The signal that one or several cells of a weighing system deliver for a specific increase of load, normally the display division, is:

Δu = (C * 1000 * U_exc * e) / (N * E_max)

Where,
Δu = Increase of signal in μV/div (micro-volts/division)
C = Nominal Sensitivity of the cell in mV/V
U_exc = Excitation Voltage of the cells in V (Volts)
e = Size of the division in kg
N = Number of load cells
E_max = Nominal capacity of the cells

Typical values:
Δu = 0,8 a 5 μV/div (micro-volts/division)
C = 1 a 3 mV/V (milli-volts per volt)
U_exc = 3 a 12 V (Volts)
e = 0,001 kg a 100 kg
N = 1 a 10
E_max = 1 kg a 400.000 kg

Example 1. Scale of Max range=15 kg, division e=0,005 kg (5g)
N = 1 cell of E_max = 20 kg, C= 2mV/V
Load Cell Excitation U_exc = 10 Volts
Δu = (2 * 1000 * 10 * 0,005) / (1 * 20 ) = 5 μV/div

Example 2. Same example as Ex.. 1) but with Load Cell Excitation at Uexc = 5 Volts
Δu = (2 * 1000 * 5 * 0,005) / (1 * 20 ) = 2,5 μV/div

Example 3. Scale of Max range= 600 kg, division e=0,200 kg
N = 4 cells of E_max = 500 kg, C= 2mV/V
Load Cell Excitation U_exc = 5 Volts
Δu = (2 * 1000 * 5 * 0,2) / (4 * 500 ) = 1 μV/div

Example 4. Scale of Max range= 1500 kg, division e=0,5 kg
N = 4 cells of E_max = 750 kg, C= 2mV/V
Load Cell Excitation Uexc = 6 Volts
Δu = (2 * 1000 * 6 * 0,5) / (4 * 750 ) = 2 μV/div

Example 5. Same scale as Ex..4) with slightly bigger cells:
N = 4 cells of Emax= 1000 kg, C= 2mV/V
Load Cell Excitation Uexc = 6 Volts

Δu = (2 * 1000 * 6 * 0,5) / (4 * 1000) = 1,5 μV/div

Example 6. Truck weighing type scale of a Max Range of =60.000 kg, division e=20 kg
N = 6 cells of Emax = 20.000 kg, C= 2mV/V
Load Cell Excitation Uexc = 10 Volts

Δu = (2 * 1000 * 10 * 20) / (6 * 20.000) = 3,3 μV/div

Example 7. Truck weighing type scale of a maximum Range =60.000 kg, division e=20 kg
N = 8 cells of Emax = 30.000 kg, C= 2mV/V
Load Cell Excitation Uexc = 6 Volts

Δu = (2 * 1000 * 6 * 20) / (8 * 30.000) = 1 μV/div

Recommendation: As we have seen in the examples above, the signal values that the cells deliver per each “display” division are very small; between 1 and 2 μV/div. Therefore, specific high sensitivity electronic instruments should be used for the load cells, that have super-stable power supply voltages, stable differential amplifiers, high resolution analog-digital converters of between 16 and 24 bits and filters and suitable protections.

The shielding of the conduit of the cell wires and a grounding of the complete system will help to protect these weak signals in environments with interferences, such as the industrial ones.